A typical feedback control system includes a plant and a controller. The plant may be a machine or other device, the operation of which is desired to be controlled. The controller receives an input reference or command signal and one or more feedback signals representative of one or more outputs of the plant. The controller, via a suitable control law, processes these signals and supplies one or more signals to the plant so that the plant operates consistent with the input command signal. Feedback control systems, such as this, have been, and continue to be, implemented in numerous and varied environments to control various types of machines. For example, most aircraft include one or more gas turbine engine control systems to control, for example, aircraft propulsion engines.
A gas turbine engine control system typically includes a plurality of actuators, a plurality of sensors, and an engine controller. The actuators are used to control the position or speed of one or more controlled components, to thereby control various engine parameters, such as fuel flow and guide vane position, that affect engine operation. The sensors measure various engine performance parameters, such as turbine rotational velocities, engine pressures, and engine temperatures, and various controlled parameters, such as fuel flow and inlet guide vane positions, and supply feedback signals representative thereof to the engine controller. The engine controller typically receives engine commands and the feedback signals from the sensors and, using a suitable engine control law, generates and supplies appropriate actuator commands to the actuators, to thereby control engine operation.
Although control systems, such as the ones described above, generally operate safely and robustly, these systems can exhibit certain drawbacks. For example, in the unlikely event that one or more of the sensor signals is lost or otherwise invalid, machine performance and/or control can be degraded. Hence, there is a need for a control system and method that can accommodate a lost or invalid sensor signal without resulting in degraded machine performance and/or control, and most notably when the machine is an aircraft gas turbine engine.